Engine revs, truck doesn't move

While driving my 2004 TrailBlazer LT, I hit the gas to accelerate
and the engine revved and didn't move. Goes into gear, you can
hear the fluid in transmission when shifting gears, fluid levels
perfect. Fluid is pretty clean. No shiny flakes in fluid. Had a guy
climb under and look, bushings are there (which I knew
because the gear shift engages), the transmission linkage
moves correctly when shifting. Did the hack with moving 4wd
and it didn't work. This transmission only has about 30,000
miles. No codes show up. After it broke down, the battery went
completely dead (was ransacked and light left on) so I
replaced the battery. It recognizes gears because you can hear
and see them shift and doors unlock in park so signals are
going to PCM. It just happened out of the blue and there were
no signs of any problems prior.